1. Field of the Invention
The present invention relates to a throttle control apparatus installed on an internal combustion engine, and more particularly to a throttle control apparatus for controlling the opening and closing action of a throttle valve by a driving source such as a motor and so on in response to an operation of an accelerator and for being able to perform various controls such as an acceleration slip control, a constant speed driving control and so on.
2. Description of the Prior Art
In an internal combustion engine which is provided with a carburetor, a throttle valve controls a mixed gas which air and fuel are mixed each other and in an internal combustion engine which is provided with an electronic controlled fuel injection apparatus, a throttle valve controls the generating power of the internal combustion engine by adjusting the intake air flow. These throttle valves are constituted so as to link with an accelerator operation mechanism including an accelerator.
In recent years, apparatuses each of which is set to open and close the throttle valve by a driving source such as a motor and so on in response to an operation of an accelerator are proposed in contrast to the above prior art in which the accelerator operation mechanism is mechanically connected with the throttle valve. An apparatus which drives a stepping motor connected with the throttle valve in response to an operation of an accelerator is disclosed, for example, in Japanese patent application laid-open publication No. 55(1980)-145867.
On the contrary, a prior measure example against the condition under which the control of an electronic controlled actuator for driving the above stepping motor is impracticable is enumerated in Japanese patent application laid-open publication No. 59(1984)-153945. For example, a throttle shaft is set to be separated from the electronic actuator by an electromagnetic clutch for closing the throttle valve by a return spring. In this prior art, however, there is not a drive means which opens-closes the throttle valve after the malfunction of control of the electronic controlled actuator and therefore there is a drawback that the vehicle can't be transfered to the suitable place for repairing. Therefore, an apparatus which overcomes the above drawback is disclosed in Japanese patent application laid-open publication No. 59(1984)-153945.
Namely, this apparatus includes an electromagnetic clutch interposed between the throttle shaft and a rotating shaft rotated by a depression of the accelerator and arranged so as to separate both shafts from each other in its exciting condition and to connect both shafts each other in its nonexciting condition and a control circuit for detecting abnormalities of operations of the electronic controlled actuator and for stopping the supply of an electric source to the electronic controlled actuator and the electromagnetic clutch by a relay. In this apparatus, the throttle shaft is mechanically connected with the accelerator via the electromagnetic clutch when the control of the electronic controlled actuator became impracticable.
Furthermore, an apparatus which overcomes the foregoing drawback of the prior apparatus disclosed in the above latter publication is disclosed in Japanese patent application laid-open publication No. 63(1988)-80039. In this apparatus, the accelerator operating portion and the throttle valve are connected each other when the amount of the throttle valve opening corresponded to the operational amount of the accelerator operating portion under the abnormal condition of the actuator and so on in contrast to the above prior apparatus which the amount of the throttle valve opening does not correspond to the operational amount of the accelerator operating portion when the accelerator operating portion and the throttle valve were connected each other. According to this apparatus, the electric current is not turned on an electromagnetic coil under the normal condition and is turned on the electromagnetic coil under the abnormal condition so as to connect the throttle valve with an accelerator link each other. And then the electric current which is turned on the electromagnetic coil is interrupted temporarily when the accelerator is released in the abnormal condition and thereby the connection between the accelerator link and a clutch disk is released. After the throttle valve has been fully closed the electromagnetic coil is excited again and thereby the accelerator link and the clutch disk are connected each other.
On the contrary, a throttle control apparatus which can maintain a predetermined amount of the throttle valve opening under the abnormal or an unexpected condition of the driving source is disclosed in Japanese patent application laid-open publication No. 2(1990)-204641. In this apparatus, namely, a connection of a clutch means between a throttle open-close means and a second driving means which is linked to the driving source is interrupted when the driving souce abnormally operated. Then, when the accelerator operation mechanism is operated more than a predetermined operation amount, the throttle open-close means is drived via a first driving means and thereby the predetermined amount of the throttle valve opening is maintained.
In the apparatus which is disclosed in the above Japanese patent application laid-open publication No.59(1984)-153945, a condition under which the control of the electronic controlled actuator becomes impracticable is detected by the additional control circuit. This control circuit stops the supplying of the electric to the electronic controlled actuator and the electromagnetic clutch. Then, the throttle shaft and the rotating shaft which is mechanically connected with the accelerator are connected with each other by the electromagnetic clutch after the control of the electronic controlled actuator is stopped. Now, even though the throttle valve is directly driven by the operation of the accelerator, the throttle valve maintains a condition which is connected with the actuator. In this situation, since the driving torque is not generated in the motor under the condition that the control of the electronic controlled actuator stops, the open-close operation of the throttle valve is obtained without hindrance in response to the operation of the accelerator.
Accordingly, the electromagnetic clutch which is used in such prior apparatus becomes large in structure and increases the cost too. Furthermore, it is necessary to take a measure so that the throttle valve is prevented from being driven continually toward the opening position by the abnormal operation of the electronic controlled actuator and so on. In the apparatus which is disclosed in the above Japanese patent application laid-open publication No.63(1988)-80039, since the electric current is set to turn on the electromagnetic coil under the abnormal condition of the actuator and so on and therefore the throttle valve is connected with the acclerator operation portion, it is not able to drive thr throttle valve by the accelerator operation when an abnormality which the electric current is not turned on the electromagnetic coil and therefore, for example, it is not able to drive the vehicle to the repair place.
On the contrary, in the apparatus which is disclosed in the above Japanese patent application laid-open publication No.2(1990)-204641, since the accelerator operation mechanism is mechanically connected with the throttle open-close means by depressing the accelerator more than the predetermined amount when an electromagnetic clutch mechanism of the clutch means becomes a condition which the electric current is not turned on and it is able to maintain the predetermined amount of the throttle valve opening, the above drawback is not caused.
Now, what is called `a traction control` is well known as a control method for preventing slips of driving wheels at a starting time or an accelerating time, namely acceleration slips. When the accelerator is carelessly depressed on snow-covered road or iced road and so on, the driving wheels slip and therefore an insufficient acceleration or a side slip are caused. According to the traction control, it is able to prevent the generation of these phenomenons. In the traction control, in general, the throttle valve of the combustion engine is driven toward closing position regardless of the operation of the accelerator by driver or a braking force is moderately applied to the drving wheels, and thereby each slip ratio of the driving wheels is controlled in a proper range.
The traction control is performed by the apparatus which is disclosed in the above Japanese patent application laid-open publication No.2(1990)-204641 too. In this apparatus, however, when the driver depresses the accelerator more than the predetermined amount while the traction control is performed, the throttle valve is opened and the predetermined amount of the throttle valve opening is obtained. Accordingly, for example, when it is required to fully close the throttle valve in the traction control, it is not able to perform the expected acceleration slip control.